Method for stabilization of soil aggregates

ABSTRACT

The present invention relates to a method for improving a soil structure by stabilization of aggregates. According to the invention it is applied to the soil a graft polymer substantially free of monomer, having an intrinsic viscosity below 1dg/l and a molecular weight below 100,000. The graft polymer is obtained by the exothermic reaction of a water soluble lignosulfonate with a member selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof. The graft polymers have been found to be also useful as binding reagents for agglomerating single particles of particulate materials. 
     The graft polymers according to the invention are obtained in the form of an aqueous solution, which may be transformed into a powder by spray drying. As soil conditioners they may be applied by spraying, alone or admixed with fertilizers or pesticides and also combined with the operation of planting and soil stabilization.

This is a division of application Ser. No. 953,799, filed Oct. 23, 1978,now U.S. Pat. No. 4,303,438, issued Dec. 1, 1981, which is acontinuation in part of Ser. No. 748,367 filed Dec. 7, 1976, nowabandoned.

The present invention relates to new lignosulfonate-based graft polymersand to methods for their manufacture. The new graft polymers have beenfound to possess many practical uses. According to a main aspect of thepresent invention it has been found that the new graft polymers haveoutstanding beneficial effects on improving the soil structure, aproperty attributed to the so-called soil conditioners, giving rise tothe formation of aggregates in the soil. According to another embodimentof the present invention the new graft polymers obtained have been foundto possess the ability of agglomerating single particles of particulatematerials into aggregates and thus changing the properties on thesurface of these materials.

As known, the structure of a soil determines a large number of itsproperties such as permebility to water, porosity, crust formation,aeration etc. An improved structure will be beneficial for theprevention of erosion by water, increase in crop yields etc. It alsosimplifies the mechanical preparation of the field before planting. Anincrease in aggregate size and in percent of aggregates will reduce winderosion. It will also induce a high penetration of rain into the soiland will improve water holding capacity and reduce evaporation, theresult of which is a better water balance in arid zones. Of specialimportance is the prevention of crust formation due to puddling by raindrops. Prevention of this puddling, allows for a better raininfiltration into the soil and causes a reduction of run-off with aconsequent erosion decrease. The crust prevention following puddling,improves germination and aeration of saplings.

It has been postulated that the differences in structure between theundesirable and the desirable types of soil are attributable todifferences in the type of the electrical charges of the individual soilparticles. Accordingly, it has been proposed to condition or to improvepoor soils, for example structurally undesirable clayey and loam soils,by applying to them certain synthetic polyelectrolytes. These are mainlybased on polyacrylamides, polymethyl-acrylonitriles, copolymers ofacrylonitriles with vinyl acetate etc. Thus, for example U.S. Pat. No.2,625,471 claims a copolymer containing 80-84% acrylonitrile, 11-15%methacrylonitrile and 5% vinyl acetate and hydrolysed in order to makeit hydrophilic. U.S. Pat. No. 2,847,392 describes a copolymer containing50% methacrylonitrile and 50% butadiene. U.S. Pat. No. 2,765,290 claimsa modification of polymethylacrylonitrile; after hydrolysis to theacidic form, the polymer is absorbed on to the surface of vermiculiteparticles and used in this form as soil conditioner.

Although these polyelectrolytes have been used successfully in a numberof limited applications, such as house gardening, they have not becomewidespread due to one or more of the following reasons:

(a) They are too expensive for large scale use.

(b) The strength of bonds holding the particles of soil in an aggregate,is too high and thus detrimental for certain properties.

(c) Very often they appear in a powder form, which causes problems intheir storage and is very inefficient in field application.

(d) Some of them have toxical properties for animals and human beings.

(e) Some of them are easily decomposed by bacteria present in the soil.

(f) Some of them are not sufficiently stable even for a complete seasonbeing readily decomposable and washed out.

Some references are encountered describing the use of lignosulfonate assoil conditioner. Some improved results are claimed to be achieved inobtaining soil aggregates using amounts of about 2% or more by weightlignosulfonate. However, such relatively large amounts of lignosulfonatebecome expensive in application as well as in manipulation and alsoraise problems concerning the bacterial activities in the soil. Thelignosulfonate is leached through the soil and thus is wasted to a largeextent. It also penetrates to certain layers where it is not needed andmay even be harmful and cause problems of contamination. Large amountsof lignosulfonate also tend to produce a massive rather than the friableaerated structure desirable in most soils for agricultural purposes. Thelignosulfonates may become irreversibly disactivated by some multivalentcations and at the same time when applied in large amounts deprive theplants from some of the necessary micro-elements.

In according with the U.S. Pat. No. 3,985,659, a graft copolymer oflignosulfonate with polyacrylate having a molecular weight of at least100,000 is utilized in drilling fluid compositions. For drilling muds,the requirement is to maintain the particles in suspension, and for thisreason these fluids should have a proper viscosity in order to impart athixotropic character to the system.

In a very recent publication, U.S.S.R. 492,261 (C.A. 84: 73052) a methodis described for improving soil structure, by mixing the soil with astructure former which is a graft polymer produced from lignosulfonatewith esters of acrylic acid and subsequently saponified to an extent of30 to 100%. The products obtained appear in the form of a viscous massand are utilized as aqueous dispersions. The inventors of the presentinvention have found that these graft polymers possess the property of agel of thixotropic nature. One disadvantage of these graft polymers isthe need for a saponification operation which adds to the process costs.Another disadvantage is their highly viscous form which requires a highdilution and consequently increases the costs of spray drying andtransforming them into powder form.

It is an object of the present invention to provide newlignosulfonate-based graft polymers which possess outstanding propertiesin stabilization of aggregates. It is yet another object of the presentinvention to provide lignosulfonate-based graft polymers which have theproperty of improving the adhesion of single particles of particulatematerials. The invention consists in a method for improving a soilstructure by stabilization of aggregates which consists of applying asoil conditioner comprising a graft polymer substantially free ofmonomer, having an intrinsic viscosity below 1 dg/l and a molecularweight lower than 100,000, said polymer being obtained by the exothermicreaction of a water soluble lignosulfonate with a member selected fromthe group consisting of acrylic acid, methacrylic acid and mixturesthereof at a pH between 1.5 to 4 in the presence of an initiator. Theratio between the lignosulfonate and the acrylic acid or methacrylicacid may be varied over a broad range being generally up to 8 parts oflignosulfonate (parts by weight) to one part (by weight) of acrylic ormethacrylic acid. The selection of the preferred ratio will be accordingto the specific end-use of the graft polymers.

According to one embodiment of the present invention, the new graftpolymers have been found to possess outstanding properties forstabilizing aggregates. For this purpose the following main advantagescan be enumerated:

(1) The new graft polymers are relatively inexpensive.

(2) Their manufacture is very simple.

(3) The amount of the relatively expensive acrylic or methacrylic acidcomponent in the graft polymer may be small.

(4) They can be applied in a high aqueous concentration, in contrast tothe relative low concentration of the acrylate esters-based graftpolymers. This has a corresponding advantage in their transportation.

The graft copolymers according to the present invention are inparticular very useful for agglomerating of clay having a particle sizebelow 2 microns, or silt having a particle size below 20 microns. Theaggregates which result have a size of above 100 microns and generallyabove a few hundreds of microns.

The preferred ratio between the components in the new graft polymer mayvary between 0.4 part to 2 parts by weight acrylic acid or methacrylicacid to one part by weight lignosulfonate. The lower limit of theacrylic component is determined by the decreased efficiency of the soilconditioner versus the price of production and costs of fieldapplication. The higher limit is determined by the relation between theincreased price of the graft polymer, due to the more expensive acryliccomponent, and the increased efficiency of the product. For specialpurposes, when the cost of the graft polymer is not critical and theneeded strength for the specific goal is high, the amount of acrylicacid or methacrylic acid monomer may be increased. A person skilled inthe art after reading the present specification will certainly be ableto determine the proper ratio between lignosulfonate and acrylic acid ormethacrylic acid in order to obtain the soil conditioner most suitablefor the purpose required. Of course the higher acrylic or methacrylicacid component in the graft polymer results in a product with a highermolecular weight and stronger bonds with the soils thus obtaining largerand stronger aggregates. It is also possible to use a mixture of two ormore graft polymers prepared separately with different ratios betweenlignosulfonate and acrylic or methacrylic acid monomers. In this mannereach conditioner in the mixture will act on the soil according to itscomposition, for the specific goal. For example if the conditioner is tobe sprayed, one may use a mixture of two types. One type would be of ahigher molecular weight for stronger bonds at the surface, the other maybe of a lower molecular weight to improve the penetration below thesurface.

The term "crude lignosulfonate" as is used in the present specification,includes the waste material resulting from the processing of plants orwood for the separation of cellulose and lignosulfonic acid or saltsthereof as obtained without any purification. The constitution of thecrude lignosulfonate varies depending on the type of plant or woodutilized and on the method of processing; it appears generally in theform of Na⁺, NH₄ ⁺ or Ca⁺⁺ salts along with various polysaccharides,which for certain uses are harmful and have to be removed. It has beenfound that the lignosulfonate salts to be utilized in the methodaccording to the present invention, may be in the crude form, which isalso less expensive than the purified form, without impairing theactivity per unit weight of the soil conditioner, but in a water solubleform and most preferably having a molecular weight of not higher than20,000. Furthermore, experiments with certain materials indicate higheractivity per unit weight of a soil conditioner produced from crudelignosulfonate than the purified form; it goes without saying howeverthat purified polysaccharide--free lignosulfonate also often referred toas lignosulfonic acid or lignosulfonate salts, may also be utilized,such as for the protection against wind and water erosion of granulatedmaterial to be used in concrete mixtures with portland cement whereinpolysaccharides may be harmful.

The graft polymerization between the acrylic acid or methacrylic acidand the lignosulfonate is an exothermic, addition reaction which occursat a pH in the range of 1.5 to 4 and preferably in the range of 2 to3.5. The products obtained are stable and even after more than one yearof storage, no change in their structure or in the results obtained fromtheir utilization were observed.

The pH is adjusted by the addition of sodium hydroxide solution orsulfuric acid according to the acidity of the reaction mixture. It hasbeen found according to the present invention that the pH has a greatinfluence on the extent of reaction as well as to the composition of theproduct. In the following Table 1, are enumerated some experimentscarried out at different pH and the reaction products are compared:

                  TABLE I                                                         ______________________________________                                        Influence of pH on the reaction product                                                                  Intrinsic                                                     % of acrylic acid                                                                             viscosity in                                       Exp.       monomer copolymerized                                                                         0.1 M sol.                                         No.  pH    with lignosulfonate                                                                           of NaCl Remarks                                    ______________________________________                                        1    1.5   99.8            0.33                                               2    2.4   99.5            0.43                                               3    6.1   10              above 1 Contains large                                                                amounts of                                                                    monomer                                    4    7     5               above 1 Contains large                                                                amounts of                                                                    monomer                                    ______________________________________                                    

Whereas at a pH in the range according to the present invention (1.5 to4) the extent of the reaction between the lignosulfonate and acrylicacid was substantially 100%, at a pH beyond the range the extent ofreaction was only 10% and 5% respectively, the products containing largeamounts of unreacted monomer. Also the appearance of the productsgreatly differs: these according to the present invention are truesolutions having a relatively low viscosity, whereas these obtained at adifferent pH range are very viscous. According to the differentproperties of such products, different uses will be envisaged. Thus forinstance, the more viscous substances will be useful for drilling mudswhere it is required to maintain small particles in suspension and avoidtheir aggregation. A typical reference can be illustrated by U.S. Pat.No. 3,985,659.

Another very important influence of the pH is on the course of thereaction. It has been found that the pH in the range of 1.5 to 4.0causes an exothermic reaction between the lignosulfonate and acrylic ormethacrylic monomer. This enables to obtain a product substantially freeof monomer and also a very quick reaction in the order of 2 to 5minutes. In FIG. 3 are given graphs on the exothermicity of the reactioncarried out at a pH in the range according to the present invention(1.40 and 2.40) and outside this range (5.10 and 6.15). The graphsclearly show that within the range according to the present inventiontemperatures of about 54° C. (at pH 2.40) and 58° C. (at pH 1.40) areobtained in about 1 minute whereas at pH outside the range claimed, thetemperatures reach a value of only about 42° C. even after 4 minutes.All these experiments were carried out at the same conditions ofconcentration and ratios lignosulfonate to acrylic acid (10%lignosulfonate in water and 1:1 ratio).

The new graft polymers obtained according to the present invention caneasily be transformed into a powder form by spray drying. The powderform of the graft polymers is of course the easiest form for handlingand transportation since it can easily be diluted to the desiredconcentration at the end use. This is an important advantage over agraft polymer obtained from an acrylic ester and lignosulfonate, whichappears as a highly viscous and thixotropic mass and more costly to bespray dried. Thus for instance the viscosity of a solution of 15% by wt.of graft polymer obtained from methyl acrylate ester and lignosulfonate(1:1) was found to be 10,000 cps (at 20 rpm) at a temperature of 25° C.while under same conditions, the same concentration of 15% by wt. of agraft polymer obtained from acrylic acid and lignosulfonate (1:1) showedonly a viscosity of 27 cps. The viscous form of the graft polymer frommethyl acrylate ester and lignosulfonate can also be illustrated by thethixotropy measurement which was found to be 5.7% (measured at 0.5 rpmwith a viscosity of 17,500 cps). This of course is in contrast to thefluidity of the new graft polymers obtained according to the presentinvention, which are obtained in the form of true solutions.

The new graft polymers according to the present invention are veryuseful as soil conditioners in stabilizing aggregates in their acidicform, such as resulting from the reaction. However, they can beneutralized to turn them less corrosive in storage and handling and alsoless sensitive to water quality. There will be differences in theirefficiency for different soils depending on the particle sizes, freesolutes in the soil and form of application. Often the efficiencypercent by weight of soil conditioner remains the same afterneutralization. Whereas the alkaline reagent utilized for theneutralization of the graft polymer is the less expensive component, anoverall advantage is thus obtained.

The neutralization can be easily carried out at room temperature,utilizing either strong or weak bases. In the latter case ammonia willbe preferred resulting also in a beneficial effect on plants growing.This is in contrast to the saponification with alkali reagents includingammonia suggested with the graft polymers obtained from esters ofacrylic acid, which must be performed at high temperature and inpressurised autoclave, which tends to be prohibitively expensive.

The initiator required to be present in the graft polymerization, isselected from known reagents used in this type of reaction e.g. hydrogenperoxide or organic peroxides such as cumene hydro-peroxide. It has beenfound that benzoyl peroxide which is also a known reagent for this typeof reaction is unsuitable for this graft copolymerization. The reasonfor this phenomenon has not yet been elucidiated. It is also possible toinitiate the polymerization reaction by purely physical means, such asultraviolet radiation.

As mentioned above there are known graft polymers of lignosulfonate withacrylic acid, containing high amounts of unreacted acrylic monomers suchas described in U.S. Pat. No. 3,985,659. These graft polymers whichappear as viscous liquids, belong to the thixotropic system and areuseful as components in drilling fluids. They are completely unsuitableas stabilizers of aggregates, their purpose being to increase theviscosity and avoiding settling of the components in the drilling mud.

Compared with the graft polymers based on acrylic esters andlignosulfonate followed by saponification, suggested as structureformers by the above mentioned Russian Pat. No. 492,261, the new graftpolymers according to the present invention are much superior as soilconditioners in stabilizing aggregates being characterised by thefollowing advantages:

1. Due to their low viscosity and high fluidity they are produced at ahigher concentration in smaller volume utensils with less energy. Theycan be utilized at higher concentrations with easy handling, which ofcourse will also save storage and transportation costs. Their lowviscosity and high fluidity also increase the shelf life of the graftpolymers.

2. They do not require saponification wherein strong alkaline solutionsand high temperatures and pressures have to be utilized, and thus aremore economical to be produced.

3. In special cases where partial or complete neutralization may bedesirable for certain types of soils, this can be performed by usingweak and inexpensive alkaline solution such as ammonium hydroxide aswell as strong alkalies at ambient temperatures and atmosphericpressure.

4. They can be easily and much more economically transformed into apowder by spray-drier than the acrylate ester-based graft polymers. Thelatter can be spray dried only after high dilution of the viscous mass(not more than 20% by wt compared of about 40% and more by wt of acrylicacid-based graft polymers), which means that much more energy would berequired for their water content evaporation.

5. No deleterious or harmful components are present in the conditionerin contrast to the methyl alcohol generated at about 13% concentrationby the hydrolysis of the methyl acrylate-based graft polymers (1:1weight ratio to lignosulfonate).

Compared with the known polyelectrolytes based on acrylonitrilecopolymers, as described in the prior art, the new graft polymersaccording to the present invention are claimed to be much superior assoil conditioners being characterized by the following improvedproperties:

1. They have a long shelf life without special storage precautions suchas dry atmosphere, darkness or oxygen-free atmosphere.

2. The molecular weight of the graft polymer according to the presentinvention is reduced and therefore the number of effective bonds perunit weight of soil conditioner is increased facilitating a more uniformspreading of the conditioner through the soil.

3. The graft polymer is more soluble and thus less sensitive to possiblefurther polymerization or setting with time.

4. The bonds formed between the graft polymer and the soil are strongenough for maintaining an aggregate of the proper magnitude, but not toostrong so as to cause the formation of large soil clods or too strongclods or not sufficiently permeable to permit adequate movement ofwater, air and nutrients into the soil treated.

5. The bonds formed are at least partially regenerative, which meansthat the aggregate property of the soil persists even after severalcycles of rain, drying and working of the soil.

6. The graft polymers are water soluble which can be easily transferredand diluted.

7. The graft polymers are not sensitive to solutions of manyelectrolytes even at high concentrations which enable use of water ofvarious qualities.

8. They are practically nontoxic.

9. Most of them can be diluted to any extent and sprayed withoutproblems of clogging the nozzles or pipes.

10. The properties of the graft polymers may be changed by varying theproportions between the acrylic or methacrylic monomer andlignosulfonate in order to provide the best result for soil conditioningaccording to the goal desired to be achieved.

Concerning the production of the new graft polymers, the processinvolved is characterized by the following advantages:

1. The main component, lignosulfonate, is a low cost raw material whichtoday is an environmental burden.

2. The process does not require the removal of the inhibitors from themonomers, as generally encountered in graft polymerization.

3. The reaction is exothermic and occurs at ambient temperatures and atatmospheric pressure. Generally the reaction time is about 5 minutes ata temperature of between 30° to 95° C.

4. The polymerization of the monomers is almost complete leaving onlytraces of monomer which may be left in the end product.

5. Tap water or even with a higher salt content may be utilized. In thisrespect emulsions obtained in the synthesis with esters of acrylic acidare more sensitive to cleaniness of the system than the solutionobtained according to the present invention.

The application of the graft polymers prepared in accordance with thepresent invention as soil conditioners can be done by the known methods.When used in the solid form, it can be mixed with the soil or spreadmechanically, watering and if necessary reworking the mixture. When usedas an aqueous solution, the soil conditioner is simply mixed with thewet soil. The soil conditioner may also be applied together with theirrigation water. The amount of soil conditioner to be given will varyfrom soil to soil in accordance with the goal envisaged; thus, forexample, for a loess-type soil, improved results in the structure, suchas increased aggregation, were obtained by using between 0.025% and 0.1%by wt of the soil. Higher amounts of soil conditioner, up to 0.2% by wt(on a dry basis) will further increase the proportion of stableaggregates, but this will generally not be economically attractive. Forsoil strengthening in construction work however, higher amounts may berecommended.

A preferred method for the application of the new graft polymers as soilconditioner, which is much simpler than the above known ways, is byspraying the aqueous solution directly on the soil. This method ofapplication for soil conditioning has become possible, thanks to theparticular properties of the copolymer obtained according to the presentinvention.

It has been found that the conditioner sprayed on to the soil forms aprotective layer which prevents aggregate breakage by action ofraindrops or wind erosion. The rate of water infiltration into the soilis maintained, preventing the formation of an impermeable crust by theimpact of raindrops. It also improves the regeneration of infiltrationcapacity after drying and thus helps in the germination of seeds.

It has been found that by repeated spraying, drying and shallowcultivation, an excellent protective mulch layer is produced which iswell aerated, reduces the evaporation from the soil and thus retains thewater, and leads to markedly improved crop yields. This has a specialimportance where crust formation by raindrop puddling is detrimental andwater supply is limited.

Instead of using pure aqueous solutions, the graft polymer solutionobtained according to the present invention, may be sprayed admixed withan aqueous fertilizer such as ammonia solution. In this manner theincorporation of the soil conditioner is carried out at the same time asthe fertilizer application, thus saving additionally an agrotechnicaloperation. In a similar manner it is also possible to incorporate thesoil conditioner in various pesticides or herbicides and apply to thesoil together with these.

According to another embodiment of the present invention, the soilconditioning apparatus can be mounted on various soil working implementsand especially on the planting machines. This apparatus consists ofdevices for spreading the graft polymer either in powder form orpreferably in an aqueous solution on to the soil. The soil with whichthe seeds are covered will already contain the conditioner reagent andthus will retain good water infiltration and good aeration prospectseven after hevy rains or irrigation. This combined operation ofsimultaneous planting and soil stabilization can be carried out by thesimple addition of the appropriate nozzles in front of, besides orbehind the planting tool. Generally speaking, the amount of soilconditioner needed for surface spraying or along with the plantingmedium is about 20 to 50 kg. per hectare of soil. Larger amounts can beused with better results. However, these are less attractive from aneconomical point of view. Thus for example a tenfold amount and evenmore will be necessary for mixing in a plow layer. It has been foundthat the application of the new graft polymer as soil conditioners canalso be carried out on an area of limited extent in strips or on patchesof soil. Better results are obtained with larger water dilution and insoil which is already humid prior to the application of the soilconditioner.

The outstanding results of soil conditioning obtained with the graftpolymers according to the present invention, were substantiated both inlaboratory and in field tests, and much better results as regards thestability of aggregates than those obtained with a known acrylic polymer(manufactured and marketed by Monsanto under the Trade mark of"Krylium") or with crude lignosulfonate were achieved. It was found thatthe beneficial effect of the new soil conditioners on aggregateformation appears even with a very low percentage of graft polymerproduced according to the present invention.

FIG. 1 illustrates in graphic form the percentage of stable aggregateslarger than 0.1 mm (by wet sieving) in a loess type soil obtained, as afunction of the percentage (by wt) of conditioner used. For comparison,corresponding tests were performed with crude lignosulfonate--given inGraph 1--and with the same "Krylium" given in Graph 2. The improvedresults of the new soil conditioner are self-evident. Whereas with anamount of 0.075% by wt. lignosulfonate or Krylium, the stable aggregateswere 37% and 45% respectively, the stable aggregates were 60% and 72%(Graphs 3, 4) when using the same amount of conditioner preparedaccording to the present invention. In Graph 3 the soil conditionerconsists of a graft polymer 0.6 parts acrylic acid, 1 partlignosulfonate (40% by wt. concentration in water) while in Graph 4--itconsists of 1 part acrylic acid and 1 part lignosulfonate (25% by wt.concentration in water).

FIG. 2 illustrates the influence of rain on rate of infiltration in aloess soil type, measured on rain intensity of 60 mm/hr. It appears thatwith untreated loess (Graph 1) the rate of infiltration decreases from22 mm/hr. to 6.8 mm/hr. after 30 minutes. With a loess spread with 1 mmdepth of a solution of 0.3% by wt conditioner (prepared according to thepresent invention), the rate of infiltration after 30 minutes decreasesonly to 21 mm/hr. (Graph 2). Another beneficial effect which has beenfound is that after the loess drying, the infiltration capacity isregenerated.

Wet sieving tests of soil aggregates were carried out on a calcareousclay soil (40% CaCO₃ and 50% clay) from Maos Haim (in the Jordan Valley)treated with the new graft polymer (prepared as described in Example 2hereinafter). As known serious structural problems concerning aggregatesformation in the size range of 0.1-2 mm are encountered in suchcalcareous soil. The results obtained are given in the following TableII:

                                      TABLE II                                    __________________________________________________________________________    % of soil                                                                     conditioner                                                                              0  0.025%                                                                              0.050%                                                                              0.075%                                                                              0.1%                                                                              0.2%                                      utilized                                                                      __________________________________________________________________________       Size of                                                                    Ord.                                                                             aggreg-                                                                    No.                                                                              ates    % of aggregates                                                    __________________________________________________________________________    1  Larger than                                                                           4.23                                                                             12.38 14.98 20.16 21.16                                                                             30.40                                        2 mm                                                                       2. From 1 mm                                                                             13.75                                                                            14.74 16.97 18.21 20.36                                                                             27.01                                        to 2 mm                                                                    3. From 0.5 mm                                                                           18.94                                                                            19.86 20.31 21.65 21.47                                                                             23.07                                        to 1 mm                                                                    4. Total larger                                                                          36.92                                                                            46.95 52.26 60.02 63.43                                                                             80.48                                        than 0.5 mm                                                                5. From 0.25 mm                                                                          22.53                                                                            21.90 21.52 17.89 19.47                                                                             13.10                                        to 0.5 mm                                                                  6. From 0.1 mm                                                                           24.90                                                                            18.97 17.64 13.38 12.12                                                                             6.42                                         to 0.25 mm                                                                 7. Total larger                                                                          84.35                                                                            87.85 91.42 91.29 95.02                                                                             100.0                                        than 0.1 mm                                                                __________________________________________________________________________

From the above Table one can see that the total of aggregates largerthan 0.1 mm (No. 7) increase by about 15% (from 84.35 to 100.0) at alevel of 0.2% soil conditioner. At first sight this seems a rather smalleffect; however, excluding the aggregate size of 0.1-0.5 mm, theincrease is about 43.5%. This indicates that the strength of the bondsformed by the soil conditioner is optimal. It fits exactly for formationof aggregates larger than 0.5 mm but below 2 mm size.

The new graft polymers obtained according to the present inventionpossessing the fundamental polyelectrolytic properties, may also beuseful for various other purposes, such as animal feed pelletizers,leather tanning, sequestering agents of metallic ions and preventingturbidity due to mud suspensions in fish ponds. It can also be utilizedin water treatment to get out suspended solids. Of special interest isthe agglomeration of particulate raw materials thus avoiding dustformation by wind erosion. This will therefore solve environmentalproblems of dust and pollution from storage, transportation and handlingof various particulate materials such as coal, sulfur, chalk, rockphosphate etc. Addition of the new graft polymers to calcium hydroxidedispersion (milk of lime) during or after its formation will preventspearing off the dried fine material. For improving the soil structure,the new graft polymers can produce larger aggregates which will be lesslikely to be eroded in pipes. Furthermore, it will trap very fine clayparticles that will move through the soil.

In order further and more fully to illustrate the nature of thisinvention and the manner of practising it, the following Examples arepresented for clearness of understanding only and no limitation shouldbe understood therefrom. The amounts used are expressed in parts byweight unless otherwise stated.

EXAMPLE 1

100 parts of crude lignosulfonate (containing polysaccharides asobtained from the paper industry) were introduced into a reactor(provided with a stirrer, a thermometer and a condenser) together with150 parts of tap water. Subsequently 60 parts of acrylic acid wereadded; the pH being adjusted by a sodium hydroxide solution (20%) to 2.5and the mixture heated to about 30° C. Then 2 parts of hydrogen peroxide(10% by volume) were added and an exothermic reaction was observed, thetemperature reaching 75° C. The reaction was kept going at thistemperature for 5 minutes and further heated and kept at 95° C. for 10minutes to ensure the completion of the reaction. The product appearedin the form of a brown solution and was very useful as a soilconditioner for alkali soils and for stabilization of sand against winderosion. The beneficial results in the formation of stable aggregates,appear in Graph 3 (FIG. 1).

EXAMPLE 2

In this Example 100 parts of crude lignosulfonate were mixed with 300parts of tap water in a similar manner as in the previous Example andheated at about 30° C. with 100 parts of acrylic acid in the presence of2 parts cumene hydroperoxide, the pH being adjusted to 2.5 as inExample 1. An exothermic reaction was observed the temperature reachingabout 80° C. To ensure the end of the polymerization the reaction waskept going at 95° C. for ten minutes. The brown solution was neutralizedwith 92 parts of an aqueous solution of NH₄ OH (25% by wt), the pH ofthe product obtained being about 6.5. It was very useful as a soilconditioner for most soils, as appears in the formation of stableaggregates in Graph 4 of FIG. 1. It was also tested on the influence ofrain on rate of infiltration in a loess soil type, the beneficialresults are presented in Graph 2 of FIG. 2.

EXAMPLE 3

The preparation as described in Example 1 was repeated using the samecrude lignosulfonate at the same concentration with 40 parts acrylicacid and 0.2 parts of cumene hydroperoxide as initiator. The otherreaction conditions were the same as in Example 1. The aqueous solutionobtained was very useful as soil conditioner, especially admixed with analkaline fertilizer such as ammonia and sprayed onto the soil.

EXAMPLE 4

The preparation as described in Example 1 was repeated using the samecrude lignosulfonate at the same concentration, with 60 partsmethacrylic acid and 2 parts hydrogen peroxide (10% by volume) andheated to about 40° C. Due to the exothermicity of the reaction, thetemperature of the reaction mixture reached 65° C. After the reactionwas kept going for about 5 minutes at this temperature, it was furtherheated at 95° C. and kept for 10 minutes to ensure the completeconsumption of the methacrylic acid. The product was a brown solutionand was useful as a soil conditioner for sandy soils.

EXAMPLE 5

The preparation as described in Example 2 was repeated using the samecrude lignosulfonate (100 parts) at the same concentration and heatedwith 100 parts methacrylic acid at 35° C. in the presence of 2 parts H₂O₂ (10% by volume). Due to the exothermicity of the reaction, thetemperature of the reaction mixture reached 75° C. After the reactionwas kept going for about 5 minutes at this temperature, it was furtherheated at 95° C. and kept for 10 minutes to ensure the completeconsumption of the metacrylic acid. The product obtained was less fluidthan that obtained in the previous Example. It was very useful in stableaggregates formation in particular for alkaline soils. If desired, itcan easily be neutralized with an ammonia solution (20%) and thus can beutilized also on neutral and acidic soils.

EXAMPLE 6

The preparation as described in the previous Example was repeated using100 parts crude lignosulfonate, 300 parts tap water with 50 partsacrylic acid and 50 parts methacrylic acid. The reaction was performedin the presence of 2 parts H₂ O₂ (10% by volume). Due to theexothermicity of the reaction, the temperature of the reaction mixturereached 70° C. After 5 minutes at this temperature, it was heated at 95°C. for further 10 minutes to ensure a complete reaction of the acrylicand methacrylic acid components.

EXAMPLE 7

Heaps of phosphate rock (-20 mesh size, Tyler scale) were sprayed by anaqueous solution containing 5 g/l of the graft polymer preparedaccording to Example 2, at a rate of 1 l/square meter. After drying, theheaps were subjected to wind erosion in a wind tunnel and it was foundthat erosion started only when the wind had a velocity of 60 Km/hr. Acomparative test carried out with water alone showed that at the samewater rate spraying, the erosion began already when the wind had avelocity of 25 Km/hr.

EXAMPLE 8

The previous Example was repeated with heaps of coal (-4 mesh size,Tyler scale) sprayed with the same reagent and rate as before. The sameimproved results against wind erosion were noticed.

A comparative qualitative test showed that the coal treated only withwater was dusty on handling.

EXAMPLE 9

A marly soil (from the Jordan Valley) was sprayed with a solution of 5%by wt of the graft polymer obtained in Example 2, using various rates ofsolution. An improved crust was obtained at a rate of 400 g graftpolymer per square meter. The crust was stable and withstood wind tunneltest at a wind velocity of 60 Km/hr. A comparative test with watershowed that the crust was stable only at a wind velocity of 30 Km/hr.

We claim:
 1. Graft polymers obtained by the exothermic reaction oflignosulfonate with a member selected from the group consisting ofacrylic acid, methacrylic acid and mixtures thereof at a pH between 1.5to 4 in the presence of an initiator, said polymers being substantiallyfree of monomer and having an intrinsic viscosity below 1 dg/l andmolecular weight lower than 100,000.
 2. Graft polymers obtainedaccording to claim 1, wherein the weight ratio between the components isup to 8 parts lignosulfonate to one part acrylic acid or methacrylicacid.
 3. Graft polymers obtained according to claim 1, wherein theinitiator used is of the peroxide type.
 4. Graft polymers obtainedaccording to claim 3, wherein the peroxide used is selected from thegroup consisting of hydrogen peroxide and cumene hydroperoxide.
 5. Graftpolymers obtained according to claim 1, wherein the lignosulfonateutilized is substantially free of polysaccharides.
 6. Graft polymersobtained by the exothermic reaction of lignosulfonate with a memberselected from the group consisting of acrylic acid, methacrylic acid andmixtures thereof at a pH between 1.5 to 4 in the presence of aninitiator and subsequently neutralized by an alkali.
 7. Graft polymersaccording to claim 6 wherein a partial or complete neutralization isperformed by an aqueous alkaline solution selected from the groupconsisting of NaOH and NH₄ OH.
 8. Graft polymers according to claim 1,obtained in a powder form by spray drying.
 9. Graft polymers accordingto claim 1, wherein the weight ratios between the components are in therange of between 1 part lignosulfonate to 0.4 part acrylic ormethacrylic acid and 1 part lignosulfonate to 2 parts acrylic acid ormethacrylic acid.